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Are Solar Windows The Next Big Renewable Breakthrough?

Windows that let in light and produce electricity at the same time: a recipe for a perfect life and an idea as fascinating as unattainable. At least until recently. Making a thin solar-cell film to stick on a window glass is easy enough. Making it convert sunlight into electricity at any meaningful level of efficiency was the hard part. And now scientists from Australia say they’ve cracked it.

The team, led by materials chemistry professor Jacek Jasieniak, developed a new kind of semi-transparent solar cell that featured one important difference from other semi-transparent cells: they had a component replaced with an organic conductor that can be transformed into a polymer, much more stable than the original—and common—solar cell component.

The original component, called Spiro-OMeTAD, is notoriously unstable, and has been known to affect adversely the way perovskite solar cells convert light into electricity. What’s a perovskite solar cell? It’s a cell that uses one of a group of minerals collectively known as perovskites instead of solicon. Perovskites can deliver higher conversion efficiency at lower cost than silicon cells. Yet stability has been a problem and the Australian team seems to have succeeded in solving this problem.

The efficiency of the new solar cells is truly impressive: “Rooftop solar has a conversion efficiency of between 15 and 20%,” says Jasieniak, as quoted by Exciton Science. “The semi-transparent cells have a conversion efficiency of 17%, while still transmitting more than 10% of the incoming light, so they are right in the zone. It’s long been a dream to have windows that generate electricity, and now that looks possible.”

There is a catch of sorts. The more opaque the glass, the more solar energy it converts into electricity, so, if the new cells are to be incorporated into buildings, architects would need to factor in the relationship between glass transparency and conversion efficiency. But that may simply mean they could plan for more glass as proportion of the building.

According to Jasieniak, a solar window using the new cells can be as transparent as existing glazed commercial windows and generate some 140 watts of electricity per square meter. If we multiply this by all the square meters an office building, for example, has available for windows, the amount of energy that these solar cells could generate becomes quite respectable.

There is also a private company in the United States that recently reported promising news about solar windows. Ubiquitous Energy makes what it calls a solar glass that can convert light into electricity without having to tint the glass. The company—a spinoff from the Massachusetts Institute of Technology—uses an organic dye for the glass that absorbs the infrared part of the spectrum radiated by the sun and turns it into electricity.

"Light absorbing dyes are found all around us. They're in paints, they're in pigments for clothing, and they're even in electronic devices," the chief technology officer of Ubiquitous Energy, Miles Barr, told CNN last month. "What we've done is we've engineered those dyes to selectively absorb infrared light and also convert that light into electricity."

The great thing about this glass, the ClearView Power glass, is that it is not just confined to buildings. It can be fitted on cars or even smartphone screens. The not so great thing is that the conversion ratio of the light-absorbing dye is relatively low. From another perspective, however, the efficiency ratio is record-high. Last year, Ubiquitous Energy boasted a world record in conversion efficiency for a transparent solar cell, at 9.8 percent.

Now, that’s certainly not a whole lot but, again, low cost and scalability could make every percent of conversion count, just as with the Australian team’s solar cell. The combination of low cost and easy scalability becomes even more attractive in the context of a drive to use more renewable energy, which has gathered such pace that California has made it mandatory for every new home to feature some form of solar technology.

The immediate future of the solar glass is uncertain. The solar industry has not avoided a blow from the coronavirus pandemic and new solar installations in California, the nation’s leader in solar power, have slumped. It was only to be expected, with the same thing happening in many other industries as lockdown-caused unemployment surges and people retrench and shrink their spending.

This year won’t be good for any renewables, according to forecasters. The industry is already bleeding jobs, and these could reach a quarter of a million people. At the same time, a lot of utility-scale projects could be delayed to the second half of 2020 and even next year.

However, the pandemic will likely be only a temporary setback for the solar industry, especially for those parts of it that offer cheaper alternatives to rooftop solar installations. Solar glass holds a lot of promise and it is only a matter of time before this promise is materialized.

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